Reference electrode for cathodic protection systems

ABSTRACT

A reference electrode for cathodic protection systems on ships and boats comprising a metal base consisting of titanium, tantalum or niobium having a surface coated with silver, the silver-coated surface being a roughened surface in the form of ridges and depressions, e.g. an embossed surface, and the roughened surface being coated with silver chloride.

United States Patent Inventor Edward P. Anderson Livingston, NJ.

Appl. No. 833,097

Filed June 13, 1969 Patented Nov. 2, I971 Assignee Engelhard Minerals &Chemicals Corporation Newark, NJ.

REFERENCE ELECTRODE FOR CATHODIC PROTECTION SYSTEMS 3 Claims, 3 DrawingFigs.

US. Cl 204/196, 204/147, 204/195, 204/290 F int. Cl (223i 13/00 Field oiSearch 204/1 T,

[56] References Cited UNITED STATES PATENTS 2,719,797 10/1955 Rosenblattet al. 204/290 F 3,022,243 2/1962 Anderson 204/196 3,081,252 3/1963Preiser et al 204/196 3,129,161 4/1964 Anderson et al.... 204/195 F3,133,873 5/1964 Miller et allv 204/196 3,488,274 1/1970 Geld 204/196Primary Examiner-T. Tung AuorneysSamuel Kahn and John G. KovalichABSTRACT: A reference electrode for cathodic protection systems on shipsand boats comprising a metal base consisting of titanium, tantalum orniobium having a surface coated with silver, the silver-coated surfacebeing a roughened surface in the form of ridges and depressions, e.g. anembossed surface, and the roughened surface being coated with silverchloride.

PATENTEDNUV 2 Ian INVIiN'I'UR EDWARD P ANDERSON AGE/y r REFERENCEELECTRODE FOR CATI'IODIC PROTECTION SYSTEMS BACKGROUND OF THE INVENTIONCathodic protection consists basically of applying an electrical currentto an anode, immersed in an electrolyte, and to the surface to beprotected as the cathode, whereby the surface potential is maintainedcathodic with respect to the electrolyte, thus preventing corrosion ofthe surface. In the case of painted metallic surfaces such as shiphulls, however, when the impressed current density exceeds a certainamount the paint film will become damaged, whereas an insufficientcurrent results in inadequate protection against corrosion. Therefore,an optimum exists and cathodic protection systems have been suggested,in which the fluctuating potential on the metallic surface iscontinuously registered and the power output to the anodes controlledaccordingly, either by manually or automatically adjusting the output.In order to register the potential on the metallic surface to beprotected, reference electrodes immersed in the electrolyte are used, inconjunction with the cathodic protection system, and which perform incooperation with the metallic surface as a voltaic cell to produce acurrent which functions to indicate the condition of the metallicsurface and whose response is utilized in a system to automaticallymonitor and adjust the output of the cathodic protection system. Thereference electrodes usually employed for such purpose are thesilver-silver chloride type electrodes. Some such electrodes are of thesilver button-type coated with silver chloride. In any case, suchelectrodes are subject to deterioration either by lack of desirablephysical strength of the silver button or a too rapid loss of the silverchloride, as by abrasion, to maintain the reference electrode potentialstability for long periods.

SUMMARY OF THE INVENTION In accordance with this invention, there isprovided a reference electrode preferably constructed to be positionableapproximately flat to the surface to be protected, e.g., a ships hull,with insulation means therebetween and of sufficient strength towithstand prolonged usage while at the same time having a compositionand construction such as will provide a copious supply of the chlorideion and which will maintain a stabilized electrical potential forextended periods.

The electrode can be in the form of a disc, washer, or a rivet having arivet head as the functioning electrode, and composed of a metal baseconsisting of titanium, tantalum or niobium having its outer surfaceroughened, e.g., embossed, or otherwise provided with such a roughenedsurface which is characterized by ridges and depressions, e.g., asurface having intersecting grooves, with the roughened surface beingcoated with a silver layer and then with a silver chloride layer whichfills the depressions and covers the ridges, the depressions functioningas a reservoir of silver chloride should the silver chloride coveringthe ridges become substantially depleted as by abrasion from the ridgesor deterioration over extended periods. The use of the particular basemetal composition is less expensive than the use of a solid silver baseand is of critical significance because when exposed to the electrolyte,e.g., by abrasion, the metal has the ability to readily form upon itselfa film of insulating oxide which will prevent the development of straycurrents which would otherwise unbalance the original stabilized currentoutput of the electrode.

DESCRIPTION OF THE DRAWINGS FIG. I illustrates a partly elevational andpartly cross-sectional side view of an electrode assembly according tothe invention,

FIG. 2 illustrates a top view of the electrode assembly along lines 2-2of FIG. 1 with the base metal being so modified that the roughenedsurface thereof is in the form of an embossed surface,

FIG. 3 illustrates an enlarged fragmentary view along lines 3-3 of FIG.2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Regarding FIG. 1, the electrodeassembly comprises a reference electrode generally designated as Iin theform of a circular disc having a circumferential marginal portion 2thereof extending downwardly and forming a flange which is embedded inan insulating platelike resin base 3 with the major portion of theelectrode surface exposable to an electrolyte. A tubular stem 4 ismounted on the insulating plate and extends outwardly of theundersurface 5. The tubular stem comprises a flanged end portion 6embedded in the resin plate. An insulated electrical conductor means 7containing electrically conducting wires 8 passes through the stem 4,which is threaded on its outer surface as at 9 for subsequent mountingthrough a ships hull by a mounting nut (not shown). The end of theinsulated conductor means passing through the stem and adjacent theundersurface of the electrodehas its conductor wires 8 electricallyconnected to the bottom surface of the electrode,-for example by weldingor soldering as at 10.

The electrode disc illustrated by FIG. 1 comprises a metal base 11 oftitanium, tantalum or niobium having its outer surface 12 in a roughenedcondition characterized by ridges and depressions, e.g., a surfacehaving intersecting grooves or otherwise being embossed as moreparticularly shown by FIGS. 2 and 3.

FIGS. 2 and 3 illustrate the invention showing the metal base 11 oftitanium, tantalum or niobium having a roughened surface, e.g., anembossed surface as illustrated, is coated, as by electroplating, toprovide an intermediate layer of silver 14 with the silver-coated layerbeing then coated with an outer layer 13 of silver chloride, as bydipping in molten silver chloride or by sprinkling silver chloridepowder on the surface and heating sufficiently to melt the silverchloride into ad herence with the roughened surface. The roughened orembossed surface of the base metal is characterized by ridges I5 anddepressions 16 with the layer of silver 14 conforming with the roughenedsurface leaving the depressions 16 as reservoirs 17 of excess silverchloride should the coatings l3 and M become abraded from the elevatedportions or ridges of the base metal and to still leave a sufficientamount of silver chloride on the electrode to maintain a copious supplyof the chloride ion and with the metal composition of the base, as abovedescribed, being capable, when exposed to the electrolyte, of readilyforming an insulating oxide film which will prevent the development ofstray currents to unbalance the original stabilized current output ofthe electrode.

The platelike resin insulating base 3 is provided with an annular groove18 inwardly adjacent to the marginal portions of the insulator plate toreceive the downwardly extending flange- 2 of the electrode 1 and thetop central portion 19 of the insulator base is slightly recessed toreceive the electrode in conformity with the shape and thickness of thedisc 1 in such manner that the surface of the electrode does not extendabove the ridge 20 on the marginal portion of the insulator base. Havingthe electrode positioned on the insulator base,.3 with the flange 2 inrecess 18, the space of the groove 18 above the flange 2 is filled withan insulating resin, e.g., an epoxy resin 21 so that the top surface ofthe electrode and the marginal portions of the platelike base aresubstantially in a common plane.

What is claimed is:

1. In a cathodic protection system, a reference electrode comprising ametal base consisting of titanium, tantalum or niobium, the metal basehaving a roughened surface characterized by ridges and depressions, alayer of silver on the roughened surface, and a layer of silver chloridecoating the silver layer, said silver chloride layer filling thesilver-coated depressions and covering the silver-coated ridges.

2. In a cathodic protection system according to claim 1, wherein thesilver-coated surface is a roughened surface characterized byintersecting grooves.

3. In a cathodic protection system according to claim 1, wherein thesilver-coated surface is an embossed surface.

2. In a cathodic protection system according to claim 1, wherein thesilver-coated surface is a roughened surface characterized byintersecting grooves.
 3. In a cathodic protection system according toclaim 1, wherein the silver-coated surface is an embossed surface.